Abstract
Abstract. Lidar measurements at Garmisch-Partenkirchen (Germany) have almost continually delivered backscatter coefficients of stratospheric aerosol since 1976. The time series is dominated by signals from the particles injected into or formed in the stratosphere due to major volcanic eruptions, in particular those of El Chichon (Mexico, 1982) and Mt Pinatubo (Philippines, 1991). Here, we focus more on the long-lasting background period since the late 1990s and 2006, in view of processes maintaining a residual lower-stratospheric aerosol layer in absence of major eruptions, as well as the period of moderate volcanic impact afterwards. During the long background period the stratospheric backscatter coefficients reached a level even below that observed in the late 1970s. This suggests that the predicted potential influence of the strongly growing air traffic on the stratospheric aerosol loading is very low. Some correlation may be found with single strong forest-fire events, but the average influence of biomass burning seems to be quite limited. No positive trend in background aerosol can be resolved over a period as long as that observed by lidar at Mauna Loa. We conclude that the increase of our integrated backscatter coefficients starting in 2008 is mostly due to volcanic eruptions with explosivity index 4, penetrating strongly into the stratosphere. Most of them occurred in the mid-latitudes. A key observation for judging the role of eruptions just reaching the tropopause region was that of the plume from the Icelandic volcano Eyjafjallajökull above Garmisch-Partenkirchen (April 2010) due to the proximity of that source. The top altitude of the ash above the volcano was reported just as 9.3 km, but the lidar measurements revealed enhanced stratospheric aerosol up to 14.3 km. Our analysis suggests for two or three of the four measurement days the presence of a stratospheric contribution from Iceland related to quasi-horizontal transport, differing from the strong descent of the layers entering Central Europe at low altitudes. The backscatter coefficients within the first 2 km above the tropopause exceed the stratospheric background by a factor of four to five. In addition, Asian and Saharan dust layers were identified in the free troposphere, Asian dust most likely even in the stratosphere.
Highlights
2006, in view of processes maintaining a residual lower- were identified in the free troposphere, Asian dust most likely stratospheric aerosol layer in absence of major eruptions, even in the stratosphere
We conclude that the increase of our integrated backscatter coefficients starting in 2008 is mostly due to volcanic eruptions with explosivity index 4, penetrating strongly into the stratosphere
A part of the Redoubt aerosol structure in the June examples was most likely advected below the thermal tropopause, in agreement with the idea of a “mixing zone” around the thermal tropopause (e.g., Gettelman et al, 2011). This interpretation is supported by the fact that on 5 and 30 June the relative humidity (RH) for both the Munich and the Innsbruck (37 km to the southeast; launches at 03:00 UTC) radiosonde stayed below 50 % above 8.5 km, which suggests the absence of cirrus clouds in the uppermost troposphere
Summary
In this study we use data from measurements with two lidar systems at IMK-IFU (until 2001 IFU, i.e., Institut fur Atmospharische Umweltforschung of the Fraunhofer Society; 47◦28 37 N, 11◦3 52 E, 730 m a.s.l.) and at the nearby high-altitude station Schneefernerhaus (47◦25 00 N, 10◦58 46 E, 2675 m a.s.l.) on the south side of Mt Zugspitze (2962 m a.s.l.), about 6.5 km to the south-west of IMKIFU. In the NDACC data base, following the format prescription, the data are not smoothed, which in the case of strong extinction leads to noise spikes in the lowest data segment within the tropopause region With this lidar system, rather small aerosol structures exceeding roughly 2 % of the Rayleigh return at 532 nm (that corresponds to a visual range of more than 400 km above 3 km) can be resolved within the free troposphere and lower stratosphere. A small interference by the magnetic field caused by the flashlamp current of the Nd:YAG pump laser (Trickl, 2010) persists This broad feature, lasting for several hundred microseconds, was determined from dark measurements, numerically smoothed and subtracted from the data, which resulted in noise-limited backscatter signals. The high sensitivity of the big aerosol lidar is important
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
